Transmission

ABSTRACT

In the transmissions of the background art, two larger-diameter gears are mounted on a final shaft thereby causing an increase in weight of the transmission. The present invention reduces the weight of a transmission by mounting only one larger-diameter gear on a final shaft. The transmission of the present invention includes an output shaft; a countershaft extending parallel to the output shaft; an intermediate shaft extending parallel to the output shaft; a forward drive gear rotatably supported relative to the countershaft; a reverse drive gear rotatably supported relative to the countershaft; a first intermediate gear rotatably supported relative to the intermediate shaft, the first intermediate gear normally meshing with the reverse drive gear; a second intermediate gear rotatably supported relative to the intermediate shaft, the second intermediate gear being interlocked with the first intermediate gear to rotate therewith; an output shaft driven gear fixed to the output shaft, the output shaft driven gear being normally meshing with the forward drive gear and the second intermediate gear; and a gear selecting and fixing device axially movably mounted on the countershaft for selectively fixing the forward drive gear and the reverse drive gear to the countershaft.

CROSS-REFERENCES TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2002-197503 filed in Japan on Jul. 5,2002, the entirety of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission, and more particularlyto a transmission for a saddle type vehicle (buggy) for operation onrough terrain.

2. Description of the Background Art

A conventional transmission of the background art is described inJapanese Patent Publication No. 63-61212, the entirety of which ishereby incorporated by reference. This transmission includes a primaryshaft, a main shaft, and a countershaft. Power is transmitted betweenthe primary shaft, main shaft and countershaft respectively, e.g., thecountershaft is a final shaft in this transmission.

In general, gears having diameters larger than the diameters of gearsmounted on front-stage shafts are mounted on rear-stage shafts, e.g., soas to sequentially reduce a rotational speed during power transmission.In the above-described transmission of the background art,larger-diameter gears are mounted on the final shaft.

More specifically, two larger-diameter gears having different diametersare fixed to the final shaft (the countershaft in the abovepublication). Two smaller-diameter gears normally meshing with the twolarger-diameter gears are rotatably supported relative to the shaft (themain shaft in the above publication) provided on the directly frontstage of the final shaft. Further, gear selecting and fixing means (agear selecting mechanism in the above publication) is provided betweenthese smaller-diameter gears. Either of these smaller-diameter gears isselected and fixed to the support shaft by the gear selecting and fixingmeans, thereby allowing the selection of any one of differentoperational conditions.

Applicants have determined that the background art suffers from thefollowing disadvantages. As mentioned above, the two larger-diametergears are mounted on the final shaft of the transmission in the relatedart, causing an increase in weight of the transmission.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings associated with thebackground art and achieves other advantages not realized by thebackground art.

An object of the present invention is to reduce the weight of thetransmission by mounting only one larger-diameter gear on the finalshaft;

One or more of these and other objects are accomplished by atransmission comprising an output shaft; a countershaft extendingparallel to the output shaft; an intermediate shaft extending parallelto the output shaft; a forward drive gear being rotatably supportedrelative to the countershaft; a reverse drive gear being rotatablysupported relative to the countershaft; a first intermediate gear beingrotatably supported relative to the intermediate shaft, the firstintermediate gear meshing with the reverse drive gear; a secondintermediate gear rotatably supported relative to the intermediateshaft, the second intermediate gear being interlocked with the firstintermediate gear to rotate therewith; an output shaft driven gear fixedto the output shaft, the output shaft driven gear meshing with theforward drive gear and the second intermediate gear; and a gearselecting and fixing device axially and movably mounted on thecountershaft for selectively fixing the forward drive gear and thereverse drive gear to the countershaft.

One or more of these and other objects are further accomplished by apower unit for a four-wheeled vehicle comprising an internal combustionengine having a crankshaft arranged with respect to a longitudinaldirection of the engine; a transmission including a main shaftoperatively engaged with the crankshaft through a torque converter and aprimary drive gear on the crankshaft and a primary driven gear on themain shaft; an output shaft; a countershaft extending parallel to theoutput shaft; an intermediate shaft extending parallel to the outputshaft; a forward drive gear being rotatably supported relative to thecountershaft; a reverse drive; gear being rotatably supported relativeto the countershaft; a first intermediate gear being rotatably supportedrelative to the intermediate shaft, the first intermediate gear meshingwith the reverse drive gear; a second intermediate gear rotatablysupported relative to the intermediate shaft, the second intermediategear being interlocked with the first intermediate gear to rotatetherewith; an output shaft driven gear fixed to the output shaft, theoutput shaft driven gear meshing with the forward drive gear and thesecond intermediate gear; and a gear selecting and fixing device axiallyand movably mounted on the countershaft for selectively engaging theforward drive gear and the reverse drive gear to the countershaft.

With this configuration, only one larger-diameter gear is mounted on thefinal shaft of the transmission as the output shaft driven gear, therebyallowing a reduction in the overall weight of the transmission.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinafter and the accompanying drawingswhich are given by Way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a side view of a four-wheeled buggy, e.g., saddle type vehiclefor operating in rough terrain, having a transmission according to apreferred embodiment of the present invention;

FIG. 2 is an elevational view of a power unit in the vehicle shown inFIG. 1;

FIG. 3 is a rear elevation of a rear crankcase of the power unit;

FIG. 4 is a longitudinal sectional view of an internal structure of acrankcase, showing a structural relationship between a crankshaft and amain shaft;

FIG. 5 is a longitudinal sectional view of the internal structure of thecrankcase, showing the structural relationship between the main shaft, acountershaft, an intermediate shaft, and an output shaft; and

FIG. 6 is a longitudinal sectional view showing a driving mechanism fora dog clutch for forward/reverse selection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described with reference tothe accompanying drawings. FIG. 1 is a side view of a four-wheeledbuggy, e.g., saddle type vehicle for operating in rough terrain, havinga transmission according to a preferred embodiment of the presentinvention. FIG. 2 is an elevational view of a power unit in the vehicleshown in FIG. 1. FIG. 3 is a rear elevation of a rear crankcase of thepower unit. FIG. 4 is a longitudinal sectional view of an internalstructure of a crankcase, showing a structural relationship between acrankshaft and a main shaft. FIG. 5 is a longitudinal sectional view ofthe internal structure of the crankcase, showing the structuralrelationship between the main shaft, a countershaft, an intermediateshaft, and an output shaft. FIG. 6 is a longitudinal sectional viewshowing a driving mechanism for a dog clutch for forward/reverseselection.

As seen in FIG. 1, a buggy includes a body frame 1, a pair of right andleft front wheels 2 provided at a front portion of the body frame 1, anda pair of right and left rear wheels 3 provided at a rear portion of thebody frame 1. A power unit 6 configured by integrating an internalcombustion engine 4 and a transmission 5 is supported by a centralportion of the body frame 1. The power unit 6 is arranged so that acrankshaft 7 extends in the longitudinal direction of the vehicle.

As will be described in greater detail hereinafter, the rotation of thecrankshaft 7 is transmitted through a main shaft 8, a countershaft 9,and an intermediate shaft 10 (each being shown in FIG. 3) to an outputshaft 11 in the transmission 5. These shafts 8, 9, 10, and 11 alsoextend parallel to the crankshaft 7 in the longitudinal direction of thevehicle. The front wheels 2 are driven by a front drive shaft 12connected to the front end of the output shaft 11, and the rear wheels 3are driven by a rear drive shaft 13 connected to the rear end of theoutput shaft 11. A steering handle 14, a fuel tank 15, and a saddle seat16 are arranged in this order from the front side of the vehicle on anupper portion of the body frame 1.

FIG. 2 is an elevational view of the power unit 6 as viewed from thefront side of the power unit 6. The power unit 6 generally includes acylinder head cover 20, a cylinder head 21, a cylinder block 22, and acrankcase 23 arranged in this order from the upper side of the powerunit 6. The crankcase 23 is divided into four parts along planesperpendicular to the crankshaft 7. That is, as partially shown in FIGS.4 and 5, the crankcase 23 includes a front crankcase cover 24, a frontcrankcase 25, a rear crankcase 26, and a rear crankcase cover 27arranged in this order from the front side of the power unit 6. In FIG.2, the front crankcase cover 24 is generally shown and the frontcrankcase 25 is slightly shown around the front crankcase cover 24.Various devices and pipes are mounted on the front surface of the frontcrankcase cover 24.

FIG. 3 is a rear elevation of the rear crankcase 26, showing thepositions of the crankshaft 7, the main shaft 8, the countershaft 9, theintermediate shaft 10, and the output shaft 11. FIGS. 4 and 5 arelongitudinal sectional views showing an internal structure of thecrankcase 23 along these shafts 7 to 11. More specifically, FIG. 4 showsthe relationship between the crankshaft 7 and the main shaft 8, and FIG.5 shows the relationship between the main shaft 8, the countershaft 9,the intermediate shaft 10, and the output shaft 11. In FIGS. 4 and 5,the arrow F indicates the front side of the crankcase 23.

FIG. 4 shows a power transmitting mechanism for the crankshaft 7 and themain shaft 8. The crankshaft 7 is rotatably supported through bearingsto the front and rear crankcases 25 and 26. An extended front end of thecrankshaft 7 is supported through a bearing to the front crankcase cover24. The crankshaft 7 is divided into front and rear sections in thelongitudinal direction. The front and rear sections of the crankshaft 7are connected at their crank webs 7 a by a crankpin 7 b. An alternator28 for producing alternating current by the rotation of the crankshaft 7is mounted on a rear end portion of the crankshaft 7 (the rear section).Reference numeral 29 denotes an oil filter provided on the frontcrankcase cover 24 for cleaning a clutch operating oil.

A torque converter 30 is mounted on a front portion of the crankshaft 7(the front section), and a primary drive gear 31 is mounted adjacent tothe torque converter 30. The primary drive gear 31 is rotatablysupported through a needle bearing 32 relative to the crankshaft 7. Thetorque converter 30 includes a pump impeller 33 fixed to the crankshaft7, a turbine runner 34 opposed to the pump impeller 33, and a stator 35.The primary drive gear 31 rotatable relative to the crankshaft 7 isconnected to the turbine runner 34, and power from the crankshaft 7 ishydraulically transmitted through the torque converter 30 to the primarydrive gear 31. A primary driven gear 36 normally meshing with theprimary drive gear 31 is fixed to a front end portion of the main shaft8. The rotation of the crankshaft 7 is transmitted through the torqueconverter, the primary drive gear 31, and the primary driven gear 36 tothe main shaft 8 with a primary speed reduction obtained by the gears 31and 36.

FIG. 5 shows a power transmitting mechanism and its relationship withthe main shaft 8, the countershaft 9, the intermediate shaft 10, and theoutput shaft 11. The main shaft 8 is rotatably supported throughbearings to the front and rear crankcases 25 and 26. A first-speed drivegear 40, a second-speed drive gear 41, and a third-speed drive gear 42different in the number of teeth according to gear ratios are mounted onthe main shaft 8. The second-speed drive gear 41 and the third-speeddrive gear 42 are fixed to the main shaft 8, and the first-speed drivegear 40 is relatively rotatably supported through needle bearings 43 tothe main shaft 8. In the following description, a gear relativelyrotatably supported through a needle bearing to a rotating shaft will bereferred to generally as an idle gear. A first-speed hydraulicmulti-plate clutch 50 is interposed between the main shaft 8 and thefirst-speed drive gear 40. The first-speed hydraulic multi-plate clutch50 has an outer member 51 fixed to the main shaft 8 and an inner member52 connected to the first-speed drive gear 40. A pressure plate 53 isaxially movably engaged in the outer member 51. The main shaft 8 has afront center hole 55 axially extending from the front end of the mainshaft 8 to an intermediate portion and a rear center hole 56 axiallyextending from the rear end of the main shaft 8 to the intermediateportion. The rear center hole 56 is slightly larger in diameter than thefront center hole 55. Thus, the front center hole 55 and the rear centerhole 56 of the main shaft 8 are not in communication with each other atthis intermediate portion. The main shaft 8 further has an operating oilsupply hole 57 communicating with the front center hole 55 and thefirst-speed hydraulic multi-plate clutch 50, and has lubricating oilsupply holes 58 communicating with the rear center hole 56 and theneedle bearings 43.

As shown in FIG. 5, an operating oil for the first-speed hydraulicmulti-plate clutch 50 is supplied from the front crankcase cover 24 sidethrough an operating oil supply pipe 59 into the front center hole 55,and is further supplied through the operating oil supply hole 57 intothe clutch 50. The operating oil supplied to the clutch 50 is introducedinto a space between the outer member 51 and the pressure plate 53. Whenthe pressure plate 53 is moved by this oil pressure to engage the clutch50, the first-speed drive gear 40 is fixed to the main shaft 8, so thatthe rotation of the main shaft 8 is transmitted to the first-speed drivegear 40. A lubricating oil to the needle bearings 43 for supporting thefirst-speed drive gear 40 is supplied from the rear center hole 56through the lubricating oil supply holes 58.

The countershaft 9 is composed of a front countershaft 9 a and a rearcountershaft 9 b integrally connected with each other. The countershaft9 is rotatably supported through bearings to the front crankcase 25, therear crankcase 26, and the rear crankcase cover 27. A first-speed drivengear 60, a second-speed driven gear 61, and a third-speed driven gear 62respectively meshing with the first-speed drive gear 40, thesecond-speed drive gear 41, and the third-speed drive gear 42 supportedto the main shaft 8 are mounted on the front countershaft 9 a. Thefirst-speed driven gear 60 is fixed to the front countershaft 9 a. Thesecond-speed driven gear 61 and the third-speed driven gear 62 are idlegears, which are rotatably supported through needle bearings 63 and 64relative to the front countershaft 9 a, respectively.

A second-speed hydraulic multi-plate clutch 65 is interposed between thefront countershaft 9 a and the second-speed driven gear 61. Athird-speed hydraulic multi-plate clutch 66 is interposed between thefront countershaft 9 a and the third-speed driven gear 62. Thesecond-speed hydraulic multi-plate clutch 65 has an outer member fixedto the front countershaft 9 a and an inner member connected to the idlegear 61, and the third-speed hydraulic multi-plate clutch 66 has anouter member fixed to the front countershaft 9 a and an inner memberconnected to the idle gear 62. These clutches 65 and 66 are similar inconfiguration and operation to the first-speed hydraulic multi-plateclutch 50 mentioned above. An operating oil for these clutches 65 and 66is supplied through operating oil supply holes 67 and 68 formed in thefront countershaft 9 a, respectively, thereby stopping idle rotation ofthe idle gears 61 and 62 to permit power transmission and effect asecond-speed or third-speed reduction. A lubricating oil to the needlebearings 63 and 64 for respectively supporting the second-speed drivengear 61 and the third-speed driven gear 62 is supplied throughlubricating oil supply holes 69 and 70 formed in the front countershaft9 a.

The front countershaft 9 a has a front center hole 78 axially extendingfrom the front end of the shaft 9 a to an intermediate portion and arear center hole 79 axially extending from the rear end of the shaft 9 ato the intermediate portion. The front center hole 78 has a stepwisediameter, and the rear center hole 79 is larger in diameter than thefront center hole 78. Thus, the front center hole 78 and the rear centerhole 79 of the front countershaft 9 a are not in communication with eachother at this intermediate portion. On the other hand, the rearcountershaft 9 b has a through center hole 80 axially extending betweenthe opposite ends of the shaft 9 b. The front end of the rearcountershaft 9 b is engaged with the rear center hole 79 of the frontcountershaft 9 a, thus making an integral rotation of the front and rearcountershafts 9 a and 9 b. The rear center hole 79 of the frontcountershaft 9 a is in communication with the through center hole 80 ofthe rear countershaft 9 b.

The supply of the operating oil to the second-speed and third-speedhydraulic multi-plate clutches 65 and 66 is performed through a doublepipe 81 inserted in the front center hole 78 of the countershaft 9 fromthe front crankcase cover 24 side. The double pipe 81 is composed of anouter pipe 8 la and an inner pipe 81 b inserted in the outer pipe 81 a.The operating oil to the second-speed hydraulic multi-plate clutch 65 issupplied through an oil passage defined between the outer pipe 81 a andthe inner pipe 81 b and through the operating oil supply hole 67. Theoperating oil to the third-speed hydraulic multi-plate clutch 66 issupplied through an oil passage defined inside the inner pipe 81 b andthrough the operating oil supply hole 68. The lubricating oil to theneedle bearing 63 for supporting the second-speed driven gear 61 issupplied from the front crankcase 25 side through an oil passage definedbetween the front countershaft 9 a and the outer pipe 81 a and throughthe lubricating oil supply hole 69. The lubricating oil to the needlebearing 64 for supporting the third-speed driven gear 62 is suppliedfrom the rear crankcase cover 27 side through the through center hole80, the rear center hole 79, and the lubricating oil supply hole 70.

A forward drive gear 71 and a reverse drive gear 72 are mounted on therear countershaft 9 b. These gears 71 and 72 are idle gears. A manuallyoperated dog clutch 73, providing a gear selecting and fixing function,is interposed between these gears 71 and 72 so that the dog clutch 73 isengageable with either the gear 71 or 72. Accordingly, either the gear71 or 72 engaged with the dog clutch 73 is selectively fixed to the rearcountershaft 9 b, thereby allowing power transmission. The rearcountershaft 9 b is formed with lubricating oil supply holes 76 and 77for respectively supplying the lubricating oil to needle bearings 74 and75 for respectively supporting the forward drive gear 71 and the reversedrive gear 72. The lubricating oil to the needle bearings 74 and 75 issupplied from the rear crankcase cover 27 side through the throughcenter hole 80 and the lubricating oil supply holes 76 and 77 of therear countershaft 9 b.

The intermediate shaft 10 is supported by the rear crankcase 26 and therear crankcase cover 27. A first intermediate gear 82 normally meshingwith the reverse drive gear 72 and a second intermediate gear 83 havinga long sleeve portion 83 a connected to the first intermediate gear 82is rotatably supported relative to the intermediate shaft 10. Thesegears 82 and 83 are idle gears. The lubricating oil to sliding portionsof the intermediate shaft 10 for sliding the first and secondintermediate gears 82 and 83 is supplied from the rear crankcase 26 sidethrough a center hole of the intermediate shaft 10 and lubricating oilsupply holes 84 of the intermediate shaft 10.

The output shaft 11 is rotatably supported through bearings to the frontcrankcase cover 24, the rear crankcase 26, and the rear crankcase cover27. The output shaft 11 extends through the front crankcase 25 in anon-contact relationship therewith. An output shaft driven gear 85normally meshing with the forward drive gear 71 and the secondintermediate gear 83 is fixed to the output shaft 11. The output shaftdriven gear 85 is driven in a forward direction or a reverse directionthrough either the gear 71 or 72 engaged with the dog clutch 73, therebyrotating the output shaft 11 in a direction adapted to the forwardrunning or reverse running of the vehicle. The reverse driving of theoutput shaft driven gear 85 is effected only when the countershaft 9 isbeing rotated at the first speed.

All of the gears in this transmission are constant-mesh type gears, andwhat gear ratio is to be selected is determined by the hydraulicmulti-plate clutches 50, 65, and 66 that is engaged. The hydrauliccontrol for these clutches 50, 65, and 66 is performed by a valve body90 (see FIG. 2) assembled as a hydraulic control unit including asolenoid valve and a pressure switching valve. As shown in FIG. 2, thevalve body 90 is mounted on the front surface of the front crankcasecover 24.

As shown in FIG. 5, the operating oil to the first-speed hydraulicmulti-plate clutch 50 is supplied from the valve body 90 through an oilpassage 91 formed in the front crankcase cover 24 and the operating oilsupply pipe 59 inserted in the front center hole 55 of the main shaft 8into the front center hole 55, and is further supplied through theoperating oil supply hole 57 to the first-speed hydraulic multi-plateclutch 50.

The operating oil to the second-speed hydraulic multi-plate clutch 65 orthe third-speed hydraulic multi-plate clutch 66 is supplied from thevalve body 90 through an oil passage 92 or 93 formed in the frontcrankcase cover 24 and the outer passage or the inner passage of thedouble pipe 81 inserted in the front center hole 78 of the countershaft9 into the front center hole 78. The operating oil is further suppliedthrough the operating oil supply hole 67 or 68 to the second-speedhydraulic multi-plate clutch 65 or the third-speed hydraulic multi-plateclutch 66.

A driving mechanism for the dog clutch 73 for selecting the forwardrunning or the reverse running of the vehicle is shown in FIGS. 3 and 6.Referring to FIG. 6, the outer surface of the dog clutch 73 is formedwith a circumferential groove 73 a, and a shift fork 100 is engaged atits forked portion with the circumferential groove 73 a of the dogclutch 73. The shift fork 100 is axially slidably engaged with a guideshaft 101. The guide shaft 101 is a fixed shaft supported to the rearcrankcase 26 and the rear crankcase cover 27. The shift fork 100 isintegrally formed with a shifter pin 102 opposite to the forked portion.The head of the shifter pin 102 is slidably engaged with a helicalgroove 103 a formed on a shift drum 103.

The helical groove 103 a of the shift drum 103 is a short grooveextending along a substantially half portion of the outer circumferenceof the shift drum 103. Accordingly, an unnecessary portion of the shiftdrum 103 is cut away for the purpose of weight reduction. The shift drum103 is supported to a drum shaft 104. A drum driven gear 105 and a shiftcam 106 are also mounted on the drum shaft 104. The shift drum 103, thedrum driven gear 105, and the shift cam 106 are joined together by aninterlocking pin 107 to restrain their relative rotation, e.g., so thatthese members 103, 105, and 106 are rotated together.

A shift spindle 108 is rotatably supported to the rear crankcase 26 andthe rear crankcase cover 27. A sector gear 109 meshing with the drumdriven gear 105 is fixed to the shift spindle 108. When the shiftspindle 108 is rotated, the drum driven gear 105, the shift drum 103,and the shift cam 106 are rotated together by the sector gear 109. Theshift spindle 108 is connected through an operating cable (not shown) toa shift lever (not shown) provided on the steering handle 14 of thevehicle, and is rotated by manually operating the shift lever.

As shown in FIG. 3, the shift cam 106 is a star plate member, and aroller 111 supported at the upper end of a shift drum stopper 110 is incontact with the outer circumference of the shift cam 106. The shiftdrum stopper 110 is pivotably supported to a in 112, and a spring 113 isengaged with the shift drum stopper 110 to normally bias the roller 111against the outer circumference of the shift cam 106. This mechanismconstitutes a rotational position holding device for the shift drum 103such that the rotational position of the shift drum 103 becomes stablewhen the roller 111 comes into contact with any one of the valleysformed on the outer circumference of the shift cam 106. There are threestable positions of the shift drum 103 corresponding to forward,neutral, and reverse conditions.

When the shift lever provided on the steering handle 14 of the vehicleis rotationally operated from a neutral position to a forward positionor a reverse position, the shift spindle 108 and the sector gear 109 arerotated together, thereby rotating the drum driven gear 105 to a stableposition given by the shift cam 106. At the same time, the shift drum103 is rotated about the drum shaft 104 together with the drum drivengear 105 by the operation of the interlocking pin 107, so that theshifter pin 102 is pushed by the inner edge of the helical groove 103 aformed on the outer circumference of the shift drum 103. As a result,the shift fork 100 supported to the guide shaft 101 is axially slid, andthe dog clutch 73 is accordingly moved in the axial direction of thecountershaft 9 through the circumferential groove 73 a of the dog clutch73. At this time, one of the projections formed at the opposite ends ofthe dog clutch 73 comes into engagement with either the forward drivegear 71 or the reverse drive gear 72 to fix the gear 71 or 72 to thecountershaft 9, thus allowing power transmission and effecting forwardor reverse running of the vehicle.

According to this preferred embodiment as described above in detail, thecountershaft and the intermediate shaft are provided parallel to theoutput shaft. The forward drive gear and the reverse drive gear arerotatably supported relative to the countershaft. The first intermediategear and the second intermediate gear are rotatably supported relativeto the intermediate shaft. The first intermediate gear is normally inmesh with the reverse drive gear, and the second intermediate gear isrotatable together with the first intermediate gear. The single outputshaft driven gear normally meshing with the forward drive gear and thesecond intermediate gear is fixed to the output shaft as a final shaft.Further, the dog clutch, performing the gear selecting and fixingfunction, is provided to selectively fix the forward drive gear and thereverse drive gear to the countershaft, thereby selecting differentoperational conditions of the vehicle. Thus, only one larger-diametergear is mounted on the final shaft of the transmission as the outputshaft driven gear, thereby allowing a reduction in weight of thetransmission.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A transmission comprising: an output shaft; a countershaft extendingparallel to said output shaft; an intermediate shaft extending parallelto said output shaft; a forward drive gear being rotatably supportedrelative to said countershaft; a reverse drive gear being rotatablysupported relative to said countershaft; a first intermediate gear beingrotatably supported relative to said intermediate shaft, said firstintermediate gear meshing with said reverse drive gear; a secondintermediate gear rotatably supported relative to said intermediateshaft, said second intermediate gear being interlocked with said firstintermediate gear to rotate therewith; an output shaft driven gear fixedto said output shaft, said output shaft driven gear meshing with saidforward drive gear and said second intermediate gear; a gear selectingand fixing device axially and movably mounted on said countershaft forselectively engaging said forward drive gear and said reverse drive gearto said countershaft; a main shaft operatively engaged with a crankshaftthrough a primary driven gear and a torque converter; a first speedhydraulic multi-plate clutch being positioned between said main shaftand a first-speed drive gear; a second speed hydraulic multi-plateclutch being positioned between said countershaft and a second-speeddriven gear; and a third speed hydraulic multi-plate clutch beingpositioned between said countershaft and a third-speed driven gear. 2.The transmission according to claim 1, wherein said output shaft drivengear is the only gear attached to said output shaft.
 3. The transmissionaccording to claim 1, wherein said gear selecting and fixing device is amanually operated dog clutch.
 4. The transmission according to claim 2,wherein said gear selecting and fixing device is a manually operated dogclutch.
 5. A power unit for a four-wheeled vehicle comprising: aninternal combustion engine having a crankshaft arranged with respect toa longitudinal direction of said engine; a transmission including a mainshaft operatively engaged with said crankshaft through a torqueconverter and a primary drive gear on said crankshaft and a primarydriven gear on said main shaft; an output shaft; a countershaftextending parallel to said output shaft; an intermediate shaft extendingparallel to said output shaft; a forward drive gear being rotatablysupported relative to said countershaft; a reverse drive gear beingrotatably supported relative to said countershaft; a first intermediategear being rotatably supported relative to said intermediate shaft, saidfirst intermediate gear meshing with said reverse drive gear; a secondintermediate gear rotatably supported relative to said intermediateshaft, said second intermediate gear being interlocked with said firstintermediate gear to rotate therewith; an output shaft driven gear fixedto said output shaft, said output shaft driven gear meshing with saidforward drive gear and said second intermediate gear, wherein saidoutput shaft driven gear is the only gear attached to said output shaft;a gear selecting and fixing device axially and movably mounted on saidcountershaft for selectively engaging said forward drive gear and saidreverse drive gear to said countershaft; a first speed hydraulicmulti-plate clutch being positioned between said main shaft and afirst-speed drive gear; a second speed hydraulic multi-plate clutchbeing positioned between said countershaft and a second-speed drivengear; and a third speed hydraulic multi-plate clutch being positionedbetween said countershaft and a third-speed driven gear.